In a vehicle such as an automobile or the like, a transmission is provided in order to convert a driving force of an internal combustion engine into a desired drive wheel force in accordance with a running state. As such a transmission, there are known a gear type transmission in which by selectively switching an engaging state of a plurality of stages of gear trains, a gear ratio is changed step by step and a driving force is extracted, a continuous variable transmission in which by increasing or decreasing rotational radii of the driving side and the driven side of a belt wound between a driving side pulley and a driven side pulley, a belt ratio is continuously changed and a driving force is extracted, and the like.
Among vehicles such as automobiles and the like, there is a vehicle having a clutch for connecting and disconnecting a driving force. As a clutch, there has been known an automatic starting clutch which is automatically coupled or removed by feeding/discharging oil pressure by a control section. As means for controlling such an automatic starting clutch, there is known a means for forcedly setting the automatic starting clutch into the complete coupling state in the case where, upon starting of a vehicle, the semi-coupling state of the automatic starting clutch, that is, a stalling (or slipping) state has continued for a predetermined time or longer.
Namely, when the semi-coupling state of the automatic starting clutch continues, there is a disadvantage such that a part of the driving energy of the internal combustion engine changes to heat energy by the sliding of the clutch, thereby causing an increase in oil temperature or burning. Therefore, in the case where the semi-coupling state of the automatic starting clutch has continued for a predetermined time or longer, the automatic starting clutch is forcedly set into the complete coupling state, thereby preventing the increase in oil temperature and the burning.
The applicant of the present invention has already developed an apparatus for controlling the automatic starting clutch (Japanese Patent Application No. 1-260653). According to this control apparatus, in the case where, upon starting of the vehicle, a stalling state of the automatic starting clutch has continued for a predetermined time or longer in a throttle state of a high opening degree, a target engine rotational speed is reduced, thereby preventing burning which would otherwise occur due to a burden of a high load on the automatic starting clutch for a long time.
As a countermeasure for preventing increases in oil temperature and burning in the case where the stalling state of the automatic starting clutch has continued upon starting of a vehicle, as mentioned above, there is a method whereby the automatic starting clutch is forcedly set into the complete coupling state in the case where the semi-coupling state of the automatic starting clutch has continued for a predetermined time or longer upon starting of the vehicle.
Explaining further in more detail, upon starting of a vehicle, the vehicle is controlled into a starting mode by a control section so as to set the automatic starting clutch into a semi-coupling state and, when a stalling time which is measured by a stall limiting timer is equal to or larger than a trigger value for the stall limiting timer, the vehicle is controlled to the driving mode by the control section so as to set the automatic starting clutch into the complete coupling state.
However, such a conventional control method pays no consideration to the state of the vehicle. Therefore, there is a disadvantage in that increases in oil temperature and burning of the automatic starting clutch due to the continuation of the semi-coupling state of the automatic starting clutch cannot be more effectively prevented.
That is, there are many cases in which, upon starting of the vehicle, even if the vehicle state is slightly jerky and a shock occurs, by promptly setting the automatic starting clutch into the complete coupling state, the vehicle can run without any problem after that. In other words, in the conventional control method, there is a disadvantage because the vehicle state is not considered, and the control of the clutch in the starting mode is vainly continued and some increases in oil temperature and burning are caused only because of the amount of time during which such clutch control continues.
On the other hand, in the case where the automatic starting clutch is in the complete coupling state as compared with the case where the automatic starting clutch is in the semi-coupling state in which the clutch slips, driving energy which is generated by the internal combustion engine can be more efficiently transferred to driving wheels, so that a motive power performance can be raised. Consequently, for instance, even if the vehicle state is slightly jerky and a shock occurs upon starting on a climbing slope road, by rapidly setting the automatic starting clutch into the complete coupling state, no problem occurs in the subsequent run.
In the conventional control method, however, since such a vehicle state is not considered, there is a disadvantage such that by setting the automatic starting clutch into the semi-coupling state even upon starting on a climbing slope road, the control of the clutch in the starting mode is continued longer than it is needed in a manner similar to the above, so that some unnecessary increases in oil temperature and burning are caused only because of the amount of time during which such clutch control continues.
It is an object of the invention to provide an automatic starting clutch control method whereby upon starting of a vehicle, by promptly setting the automatic starting clutch into the complete coupling state in consideration of the state of the vehicle, it is possible to prevent a semi-coupling state of the automatic starting clutch that vainly continued, so that increases in oil temperature of the automatic starting clutch and burning thereof can be more effectively prevented.
In an attempt to accomplish the above object, according to the invention, there is provided an automatic starting clutch control method whereby upon starting of a vehicle, the vehicle is controlled to a starting mode by a control section so as to set an automatic starting clutch into a semi-coupling state and, when a stalling time which is measured by a stall limiting timer is equal to or larger than a trigger value for the stall limiting timer, the vehicle is controlled to a driving mode by the control section so as to set the automatic starting clutch into a complete coupling state, characterized in that in the case where the stalling time which is measured by the stall limiting timer is equal to or larger than a trigger value for a starting mode elapsed time of the starting mode and a clutch output rotational speed of the automatic starting clutch is equal to or larger than a trigger value for the clutch output rotational speed, even before the stalling time which is measured by the stall limiting timer reaches the trigger value for the stall limiting timer, the vehicle is controlled to the driving mode by the control section so as to set the automatic starting clutch into the complete coupling state.
According to the construction of the invention, in the case where the stalling time which is measured by the stall limiting timer is equal to or larger than the trigger value for the starting mode elapsed time of the starting mode and the clutch output rotational speed of the automatic starting clutch is equal to or larger than the trigger value for the clutch output rotational speed, even before the stalling time which is measured by the stall limiting timer reaches the trigger value for the stall limiting timer, the vehicle is controlled to the driving mode by the control section so as to set the automatic starting clutch into the complete coupling state, so that the control of the starting mode is not vainly continued and the automatic starting clutch can be promptly set into the complete coupling state in consideration of the vehicle state upon starting of the vehicle.
As a method of controlling an automatic starting clutch which uses a continuous variable transmission, for instance, there have been disclosed control methods in JP-A-57-186656, JP-A-59-43249, JP-A-59-77159, and JP-A-61-233256.
The applicant of the present invention has already filed the aforementioned Japanese Patent Application No. 1-260653, in which a stall limiting timer STLTM is provided to prevent that the starting Control is continued without any limitation and, when a value of the stall limiting timer STLTM is equal to or larger than a trigger value STLTMI of the stall limiting timer, a duty (DUTY, OPWCLU) of a clutch solenoid is gradually reduced to 0%. The trigger value STLTMI of the stall limiting timer is always set to a predetermined value irrespective of the state of the transmission, the duty OPWCLU of the clutch solenoid is gradually decreased to prevent the occurrence of a large shock or an engine stop, and a sudden coupling of the clutch is prevented.
In the conventional automatic starting clutch control method, since the trigger value STLTMI of the stall limiting timer has been set to a unique value, when oil pressure is high, the amount of oil which leaks from each oil passage increases, an amount of oil which is used to clean the clutch also decreases due to leakage, and the clutch is not sufficiently cleaned.
In the case of a deteriorated clutch, friction between a clutch plate and a clutch disk becomes weak and there is a tendency such that the starting control is continued for a longer time as compared with that in the case of the normal clutch. Upon starting by the deteriorated clutch, the oil temperature rises earlier than that in the case of the normal clutch.
Therefore, there is an inconvenience in that increases in oil temperature and burning of the clutch cannot be prevented from a viewpoint of the above two items.
There is also an inconvenience in that, by forcedly coupling the clutch upon starting on a climbing slope road or the like, a shock occurs upon coupling of the clutch and it becomes uncomfortable to ride in the vehicle.
That is, in the case where the starting operation has been performed in a state in which the wheels had sufficiently been braked or in the case where the vehicle has been started on a climbing slope road, the starting control continues for a long time, and a part of the energy applied to the clutch is converted into the heat due to the sliding of the clutch, so that the oil temperature rises and the clutch is burnt.
As a countermeasure for the above problems, a time limit is provided for the starting control and the control to forcedly couple the clutch is executed. However, such a control is performed on the basis of only a result of discrimination concerning whether a predetermined time has elapsed or not irrespective of the state of the transmission. There is a fear that a shock or engine stop may occur upon forced coupling of the clutch. It is desirable to reduce the occurrence of the shock or the engine stop in a state excluding the stalling state.
To eliminate the above disadvantages, it is another object of the invention to provide an automatic starting clutch control method in which an oil temperature sensor to detect oil temperature in an oil pan is provided and, when the oil temperature is high as indicated by a detection signal from the oil temperature sensor, a trigger value is reduced, and when a starting control time as measured by a stall limiting timer is equal to or larger than the trigger value, starting control is stopped by a control unit and the automatic starting clutch is coupled, so that the trigger value can be changed in accordance with the oil temperature, an increase in oil temperature in the starting control can be prevented, and a burning of the clutch can be reduced.
In an attempt to accomplish the above object, according to the invention, there is provided an automatic starting clutch control method in which a stall limiting timer to measure a starting control time is provided and, when the starting control time is equal to or larger than a predetermined trigger value on the basis of a measurement signal from the stall limiting timer, starting control is stopped by the control unit and the automatic starting clutch is coupled, characterized in that an oil temperature sensor to detect the temperature of oil in the oil pan is provided, and when the oil temperature rises as indicated by a detection signal from the oil temperature sensor, the trigger value is reduced, and when the starting control time is equal to or larger than the trigger value on the basis of the measurement signal from the stall limiting timer, the starting control is stopped by the control unit and the automatic starting clutch is coupled.
According to the invention as mentioned above, when the oil temperature is high, the trigger value is reduced, and when the starting control time is equal to or larger than the reduced trigger value, the starting starting clutch is coupled. The trigger value is changed in accordance with the oil temperature, increases in oil temperature in the starting control are prevented, and burning of the clutch is reduced.